Chip begins to think it would be great to be an older brother, so he wishes for a little sister. After the new Hawkins family move into the vacant house across the street, a wild sequence of events results from an improbable case of mistaken identity -- an infant is somehow confused with a leg of lamb left in the boot of Steve's station wagon.

With Steve away in Seattle on a business trip, the Douglas household's version of man's best friend has been known to drag home anything he can get his jaws into. This time Tramp slinks in with a large stick of dynamite that has somewhere and somehow survived since the end of the Second World War.